Stations in wireless communication networks can be equipped with multiple antennas at transmitters and receivers to improve data rates and reliability. Wider transmission bandwidths increase capacity but lead to frequency-selective fading, and time-varying multipath fading due to station mobility and Doppler spread.
To cope with time-selective and frequency-selective fading, it is important to use transmission formats such as orthogonal frequency division multiplexing (OFDM), or single-carrier frequency division multiple access (SC-FDMA). In the context of multiuser cellular networks, OFDMA access in an uplink (UL) channel from mobile stations (MS) to a base station (BS) leads to interference avoidance for in-cell MS, and interference averaging for out-of-cell MS.
Due to cost, complexity and size reasons, the number of transmit/receive antennas in mobile stations is typically between 1 and 4, which makes exploitation of MIMO gains difficult. In the context of infrastructure-less networks, such as mobile ad hoc networks, with a single antenna at the MS, the overall network performance is significantly decreased on channels with little time and frequency selectivity due to lack of spatial diversity.